Anode for electrolysis and method of preparing the same

ABSTRACT

Provided is an anode for electrolysis having reduced overvoltage and improved lifetime while exhibiting high efficiency, and a method of preparing the same. Because the anode for electrolysis is prepared by electrostatic spray deposition, an active material can be uniformly distributed in a catalyst layer, and thus, an overvoltage can be reduced and lifetime can be improved while exhibiting high efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos.10-2017-0106463, filed on Aug. 23, 2017, and 10-2018-0093811, filed onAug. 10, 2018, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to an anode for electrolysis havingreduced overvoltage and improved lifetime while exhibiting highefficiency and a method of preparing the same.

BACKGROUND ART

Techniques for producing hydroxides, hydrogen, and chlorine byelectrolysis of low-cost brine, such as sea water, are widely known, andan electrolysis process, which is also called a chlor-alkali process,can be referred to as a process that has already proven its performanceand technical reliability in commercial operation for several decades.

With respect to the electrolysis of brine, an ion exchange membranemethod, in which an ion exchange membrane is installed in anelectrolytic bath to divide the electrolytic bath into a cation chamberand an anion chamber and brine is used as an electrolyte to obtainchlorine gas at an anode and hydrogen and caustic soda at a cathode, iscurrently the most widely used method.

Specifically, the electrolysis of brine is performed by reactions asshown in the following electrochemical reaction formulae.

2Cl⁻→Cl₂+2e ⁻(E⁰=+1.36 V)  Anodic reaction:

2H₂O+2e ⁻→2OH⁻+H₂(E⁰=−0.83 V)  Cathodic reaction:

2Cl⁻+2H₂O→2OH⁻+Cl₂+H₂(E⁰=−2.19 V)  Total reaction:

In the electrolysis of brine, an overvoltage of the anode, anovervoltage of the cathode, a voltage due to resistance of the ionexchange membrane, and a voltage due to a distance between the anode andthe cathode must be considered for an electrolytic voltage in additionto a theoretical voltage required for brine electrolysis, and theovervoltage caused by the electrode among these voltages is an importantvariable.

Thus, methods capable of reducing the overvoltage of the electrode havebeen studied, wherein, for example, a noble metal-based electrode calleda DSA (Dimensionally Stable Anode) has been developed and used as theanode and development of an excellent material having durability and lowovervoltage is required for the cathode.

Currently, an anode having a mixed oxide catalyst layer of ruthenium(Ru), iridium (Ir), and titanium (Ti) is the most widely used incommercial brine electrolysis, and the anode is advantageous in that itexhibits excellent chlorine generating reaction activity and stability,but there is a limitation in that it consumes a lot of energy duringoperation due to a high overvoltage and is limited for long-term use.

Therefore, there is a need to develop an anode having reducedovervoltage and improved lifetime as well as excellent chlorinegenerating reaction activity and stability in order for the anode to beeasily applied to the commercial brine electrolysis.

DISCLOSURE OF THE INVENTION Technical Problem

An aspect of the present invention provides an anode for electrolysishaving reduced overvoltage and improved lifetime while exhibiting highefficiency.

Another aspect of the present invention provides a method of preparingthe anode for electrolysis.

Technical Solution

According to an aspect of the present invention, there is provided ananode for electrolysis including a metal base; and a catalyst layerformed on at least one surface of the metal base, wherein the catalystlayer contains ruthenium oxide, iridium oxide, palladium oxide, andtitanium oxide, and, when the catalyst layer is equally divided into aplurality of pixels, a standard deviation of iridium compositions of theplurality of divided pixels is 0.35 mol % or less.

According to another aspect of the present invention, there is provideda method of preparing the anode for electrolysis which includes acoating step in which a composition for forming a catalyst layer iscoated on at least one surface of a metal base, dried, and heat-treated,wherein the coating is conducted by electrostatic spray deposition, andthe composition for forming a catalyst layer includes a ruthenium oxideprecursor, an iridium oxide precursor, a palladium oxide precursor, anda titanium oxide precursor.

Advantageous Effects

Since an anode for electrolysis according to the present invention isprepared by electrostatic spray deposition, an active material can beuniformly distributed in a catalyst layer, and thus, an overvoltage canbe reduced and lifetime can be improved while exhibiting highefficiency.

Also, since a method of preparing an anode for electrolysis according tothe present invention is performed by the electrostatic spray depositionwhen coating a metal base with a composition for forming a catalystlayer, the composition for forming a catalyst layer can be uniformlydistributed on an entire surface of the metal base, and thus, an anodefor electrolysis can be prepared in which the active material isuniformly distributed in the catalyst layer.

Thus, the anode for electrolysis according to the present invention andthe method of preparing the same can be suitable for industries thatneed them, particularly, brine electrolysis.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings attached to the specification illustratepreferred examples of the present invention by example, and serve toenable technical concepts of the present invention to be furtherunderstood together with detailed description of the invention givenbelow, and therefore the present invention should not be interpretedonly with matters in such drawings.

FIG. 1 is a graph showing the results of measuring a voltage of an anodeaccording to an embodiment of the present invention by constant currentchronopotentiometry.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail toallow for a clearer understanding of the present invention.

It will be understood that words or terms used in the specification andclaims shall not be interpreted as the meaning defined in commonly useddictionaries. It will be further understood that the words or termsshould be interpreted as having a meaning that is consistent with theirmeaning in the context of the relevant art and the technical idea of theinvention, based on the principle that an inventor may properly definethe meaning of the words or terms to best explain the invention.

The present invention provides an anode for electrolysis having reducedovervoltage and improved lifetime.

The anode for electrolysis according to an embodiment of the presentinvention includes a metal base; and a catalyst layer formed on at leastone surface of the metal base, wherein the catalyst layer containsruthenium oxide, iridium oxide, palladium oxide, and titanium oxide,and, when the catalyst layer is equally divided into a plurality ofpixels, a standard deviation of iridium compositions of the plurality ofdivided pixels is 0.35 mol % or less.

Specifically, the anode for electrolysis has a standard deviation ofiridium compositions of 0.2 mol % or less.

The standard deviation of iridium compositions in the present inventiondenotes uniformity of an active material in the catalyst layer, that is,a degree to which the active material is uniformly distributed in thecatalyst layer, wherein the small standard deviation means that theuniformity of the active material in the catalyst layer is excellent.

Specifically, the anode for electrolysis according to the embodiment ofthe present invention can be prepared by a preparation method to bedescribed later which includes a coating step, in which a compositionfor forming a catalyst layer is coated on at least one surface of themetal base, dried, and heat-treated, wherein the coating is conducted byelectrostatic spray deposition. Thus, with respect to the anode forelectrolysis, the active material can be uniformly distributed in thecatalyst layer, and, as a result, an overvoltage can be reduced andlifetime can be increased. In this case, the active material can includea mixed oxide of ruthenium oxide, iridium oxide, palladium oxide, andtitanium oxide.

Herein, the anode for electrolysis is equally divided into a pluralityof pixels, a mol % of iridium in each divided pixel is measured, and thestandard deviation of iridium compositions is calculated from themeasured values.

Specifically, the anode for electrolysis was fabricated to have a sizeof 1.2 m in length and 1.2 m in width (length×width=1.2 m×1.2 m), it wasequally divided into 9 pixels, and a mol % of iridium in each pixel wasthen measured using an X-ray fluorescence (XRF) analyzer. Thereafter,dispersion (V(x)) was obtained by the following Equation 1 using theeach iridium mol % obtained, and a standard deviation (σ) was obtainedby the following Equation 2 using the dispersion.

V(x)=E(x ²)−[E(x)]²  [Equation 1]

σ=√{square root over (V(x))}  [Equation 2]

In Formula 1, E(x²) represents a mean value of squared mol % of iridiumin the 9 pixels, and [E(x)]² represents a squared value of mean mol % ofiridium in the 9 pixels.

Also, the anode for electrolysis according to the embodiment of thepresent invention can contain 7.5 g or more of ruthenium metal per unitarea (m²) of the catalyst layer, and, accordingly, an anodic reactionovervoltage can be further reduced.

As described above, the catalyst layer can contain ruthenium oxide,iridium oxide, titanium oxide, and palladium oxide, and, in this case,the ruthenium oxide, the iridium oxide, the titanium oxide, and thepalladium oxide can be contained in a molar ratio of 25:10:35:2 to35:25:50:15.

Also, the catalyst layer can contain the palladium oxide in a molarratio of 2 to 20 based on total moles of the ruthenium oxide, theiridium oxide, and the titanium oxide. Specifically, the catalyst layercan contain the palladium oxide in a molar ratio of 8 to 12 based on thetotal moles of the ruthenium oxide, the iridium oxide, and the titaniumoxide. In a case in which the catalyst layer includes the palladiumoxide in the above ratio, an overvoltage during anodic reaction of theanode for electrolysis including the same can be further reduced.

Furthermore, the anode for electrolysis according to another embodimentof the present invention includes a metal base; and a catalyst layerformed on at least one surface of the metal base, wherein the catalystlayer contains a platinum group oxide and titanium oxide, wherein theplatinum group oxide includes ruthenium oxide, iridium oxide, andpalladium oxide, a molar ratio of the platinum group oxide to thetitanium oxide is in a range of 90:10 to 40:60, a molar ratio of theruthenium oxide to the iridium oxide is in a range of 90:10 to 50:50,and a molar ratio of the palladium oxide to the ruthenium oxide and theiridium oxide is in a range of 5:95 to 40:60, and, when the catalystlayer is equally divided into a plurality of pixels, a standarddeviation of iridium compositions of the plurality of divided pixels is0.35 mol % or less, and the anode can be operated with high currentefficiency to generate 8 g/l or more of hypochlorite.

Herein, the standard deviation of the iridium compositions can beobtained by the method as described above.

The catalyst layer can further contain niobium oxide, if necessary.

The metal base can include titanium, tantalum, aluminum, hafnium,nickel, zirconium, molybdenum, tungsten, stainless steel, or an alloythereof, and can specifically be titanium.

Also, the anode for electrolysis according to the embodiment of thepresent invention can be used as an electrolysis electrode of an aqueoussolution containing chloride, particularly, an anode. Furthermore, theaqueous solution containing chloride can be an aqueous solutioncontaining sodium chloride or potassium chloride.

Also, the anode for electrolysis according to the embodiment of thepresent invention can be used as an anode for preparing hypochlorite orchlorine. For example, the anode for electrolysis can generatehypochlorite or chlorine by being used as an anode for brineelectrolysis.

Furthermore, the present invention provides a method of preparing theanode for electrolysis.

The method of preparing the anode for electrolysis according to anembodiment of the present invention includes a coating step (Step A), inwhich a composition for forming a catalyst layer is coated on at leastone surface of a metal base, dried, and heat-treated, wherein thecoating is conducted by electrostatic spray deposition in which anamount of the composition for forming a catalyst layer per spray and aspray rate are respectively adjusted to be in ranges of 50 ml to 80 mland 20 ml/min to 35 ml/min, and the composition for forming a catalystlayer includes a ruthenium oxide precursor, an iridium oxide precursor,a palladium oxide precursor, and a titanium oxide precursor.

Step A is a step for preparing an anode for electrolysis by forming acatalyst layer on at least one surface of a metal base, wherein it canbe performed by coating the at least one surface of the metal base withthe composition for forming a catalyst layer, drying, and performing aheat treatment.

The electrostatic spray deposition is a method in which fine coatingliquid particles charged by a constant current are coated on asubstrate, wherein a spray nozzle is mechanically controlled to be ableto spray the composition for forming a catalyst layer on at least onesurface of the metal base at a constant rate, and thus, theelectrostatic spray deposition can allow the composition for forming acatalyst layer to be uniformly distributed on the metal base.

Specifically, the coating is conducted by electrostatic spraydeposition, wherein the coating can be conducted so that the compositionfor forming a catalyst layer is sprayed in an amount per spray of 50 mlto 80 ml at a rate of 20 ml/min to 35 ml/min, for example, 25 ml/min. Inthis case, the amount per spray is an amount required to spray bothsides of the metal base once, and the coating can be performed at roomtemperature.

In general, an anode for electrolysis is prepared by forming a catalystlayer containing an anodic reaction active material on a metal base,and, in this case, the catalyst layer is formed by coating a compositionfor forming the catalyst layer containing an anodic reaction activematerial on the metal base, drying, and performing a heat treatment. Inthis case, the coating can typically be performed by doctor blading, diecasting, comma coating, screen printing, spray coating, roller coating,and brushing, wherein, in this case, a uniform distribution of theactive material on the metal base is difficult, the active material maynot be uniformly distributed in the catalyst layer of the anode thusprepared, and, as a result, activity of the anode can be reduced orlifetime can be reduced.

However, in the preparation method according to the embodiment of thepresent invention, since the composition for forming a catalyst layer iscoated on the metal base by the electrostatic spray deposition insteadof the conventional method as described above, an anode can be preparedin which the active material is uniformly distributed in the catalystlayer, and, accordingly, with respect to the anode for electrolysisprepared by the method, the overvoltage can not only be reduced, but thelifetime can also be improved.

The preparation method can include a step of performing a pretreatmentof the metal base before the composition for forming a catalyst layer iscoated on the at least one surface of the metal base, and, in this case,the pretreatment can include the formation of irregularities on thesurface of the metal base by chemical etching, blasting or thermalspraying.

Specifically, the pretreatment can be performed by blasting the surfaceof the metal base to form fine irregularities, performing a salttreatment, and then performing an acid treatment. For example, in anembodiment of the present invention, the pretreatment was performed insuch a manner that the surface of the metal base was sandblasted withaluminum oxide to have a structure with irregularities, immersed in a 50vol % sulfuric acid aqueous solution at 80° C. for 2 hours, washed withdistilled water, and then dried.

Also, the metal base is not particularly limited, but can have athickness of 50 μm to 500 μm.

The composition for forming a catalyst layer can be prepared bydissolving the ruthenium oxide precursor, the iridium oxide precursor,the palladium oxide precursor, and the titanium oxide precursor in analcohol solution.

The alcohol solution is not particularly limited, but can, for example,be n-butanol.

Herein, the ruthenium oxide precursor, the iridium oxide precursor, thepalladium oxide precursor, and the titanium oxide precursor respectivelyrepresent substances that change to ruthenium oxide, iridium oxide,palladium oxide, and titanium oxide, wherein these precursors are notparticularly limited, but the precursors can be those conventionallyused in the art, and, for example, can include a hydrate, hydroxide,chloride, or oxide of each metal.

For example, the ruthenium oxide precursor can be ruthenium chloridehydrate (RuCl₃.xH₂O), the iridium oxide precursor can be iridiumchloride hydrate (IrCl₃.xH₂O), the palladium oxide precursor can bepalladium chloride or palladium chloride hydrate (PdCl₂.xH₂O), and thetitanium oxide precursor can be titanium isopropoxide.

Also, the composition for forming a catalyst layer can further include aniobium oxide precursor, and the niobium oxide precursor represents asubstance that changes to niobium oxide, wherein the niobium oxideprecursor can include a hydrate, hydroxide, chloride, or oxide ofniobium.

The composition for forming a catalyst layer can include each metaloxide precursor so that a composition of each metal oxide in thecatalyst layer formed from the composition is within the above-describedrange.

The drying can be performed at 50° C. to 200° C. for 5 minutes to 60minutes, and can be specifically performed at 50° C. to 100° C. for 5minutes to 20 minutes.

Also, the heat treatment can be performed at 400° C. to 600° C. for 1hour or less, and can be specifically performed at 450° C. to 500° C.for 10 minutes to 30 minutes. In a case in which the heat treatment isperformed under the above-described temperature condition, it may notaffect a decrease in strength of the metal base while impurities in thecatalyst layer are easily removed. Furthermore, since an excessivelyhigh temperature condition is not required, energy consumption can bereduced, and thus, economic efficiency can be excellent.

The coating can be performed by sequentially repeating coating, drying,and heat-treating of the composition for forming a catalyst layer sothat an amount of ruthenium metal per unit area (m²) of the metal baseis 7.5 g or more. That is, after the composition for forming a catalystlayer is coated on at least one surface of the metal base, dried, andheat-treated, the preparation method according to the embodiment of thepresent invention can be performed by repeatedly coating, drying, andheat-treating the one surface of the metal base which has been coatedwith the first composition for forming a catalyst layer.

Hereinafter, the present invention will be described in more detailaccording to examples and experimental examples. However, the followingexamples and experimental examples are merely presented to exemplify thepresent invention, and the scope of the present invention is not limitedthereto.

Example 1

After a surface of titanium was sandblasted with aluminum oxide (120mesh) at a pressure of 0.4 MPa to have a structure with irregularitiesand washed to remove oil and impurities, fine irregularities were formedon the surface by immersing the titanium in a 50 vol % sulfuric acidaqueous solution at 80° C. for 2 hours, and the surface was washed withdistilled water to prepare a titanium base.

Ruthenium chloride hydrate, iridium chloride hydrate, palladiumchloride, and titanium isopropoxide were added to 600 ml of n-butanoland mixed to prepare a composition for forming a catalyst layer. In thiscase, the composition included Ru, Ir, Ti, and Pd in a molar ratio of27:20:45:8 based on metal components.

Both surfaces of the titanium base were coated with the preparedcomposition for forming a catalyst layer. In this case, the coating wasconducted by electrostatic spray deposition at room temperature, inwhich the composition for forming a catalyst layer was added ton-butanol at a dilution ratio of 1/3 (50 g/l), an amount of thecomposition per spray was 80 ml, and a spray rate was 25 ml/min.

After the coating, the coated titanium base was dried for 10 minutes ina convection drying oven at 70° C. and was then heat-treated for 10minutes in an electric heating furnace at 480° C. In this case, thecoating, drying, and heat treatment of the composition for forming acatalyst layer were repeated until an amount of ruthenium per unit area(1 m²) of the titanium base became 7.5 g. The final heat treatment wasperformed at 480° C. for 1 hour to prepare an anode.

Example 2

An anode was prepared in the same manner as in Example 1 except thatcoating of the composition for forming a catalyst layer was conducted byelectrostatic spray deposition at room temperature in which a dilutionratio was 1/2 (75 g/l), an amount of the composition per spray was 50ml, and a spray rate was 25 ml/min.

Comparative Example 1

After a surface of titanium was sandblasted with aluminum oxide (120mesh) at a pressure of 0.4 MPa to have a structure with irregularitiesand washed to remove oil and impurities, fine irregularities were formedon the surface by immersing the titanium in a 50 vol % sulfuric acidaqueous solution at 80° C. for 2 hours, and the surface was washed withdistilled water to prepare a titanium base.

Ruthenium chloride hydrate, iridium chloride hydrate, palladiumchloride, and titanium isopropoxide were added to 600 ml of n-butanoland mixed to prepare a composition for forming a catalyst layer. In thiscase, the composition included Ru, Ir, Ti, and Pd in a molar ratio of27:20:45:8 based on metal components.

One surface of the titanium base was coated with the preparedcomposition for forming a catalyst layer, was dried for 10 minutes in aconvection drying oven at 70° C., and was then heat-treated for 10minutes in an electric heating furnace at 480° C. In this case, thecoating, drying, and heat treatment of the composition for forming acatalyst layer were repeated until an amount of ruthenium per unit area(1 m²) of the titanium base became 7.5 g, and the final heat treatmentwas performed at 480° C. for 1 hour to prepare an anode.

Comparative Example 2

An anode was prepared in the same manner as in Example 1 except thatcoating of the composition for forming a catalyst layer was conducted byelectrostatic spray deposition at room temperature in which a dilutionratio was 1/2 (75 g/l), an amount of the composition per spray was 40ml, and a spray rate was 25 ml/min.

Comparative Example 3

An anode was prepared in the same manner as in Example 1 except thatcoating of the composition for forming a catalyst layer was conducted byelectrostatic spray deposition at room temperature in which a dilutionratio was 1/3 (50 g/l), an amount of the composition per spray was 90ml, and a spray rate was 25 ml/min.

Experimental Example 1

A degree of uniform distribution of metal in the catalyst layer of eachanode prepared in the examples and comparative examples wascomparatively analyzed, and the results thereof are presented in Table 1below.

Specifically, each anode was fabricated to have a size of 1.2 m inlength and 1.2 m in width, it was equally divided into 9 pixels, and amol % of iridium in each pixel was then measured using an X-rayfluorescence (XRF) analyzer. Thereafter, a mean value and dispersionwere obtained by using the each iridium mole % obtained, and a standarddeviation was obtained by using the dispersion.

TABLE 1 The number of coating repetitions Mean value Standard deviationCategory (number of times) (mol %) (mol %) Example 1 11 5.11 0.31Example 2 9 4.64 0.191 Comparative 12 4.82 0.48 Example 1 Comparative 124.81 0.40 Example 2 Comparative 9 4.94 0.51 Example 3

As illustrated in Table 1, with respect to the anodes of Examples 1 and2 according to the embodiment of the present invention, the standarddeviations of iridium compositions in the catalyst layer were small atless than 0.35 mol %, but, with respect to Comparative Example 1, thestandard deviation was significantly increased.

Also, with respect to the anodes of Comparative Examples 2 and 3 inwhich the compositions for forming a catalyst layer were coated byelectrostatic spray deposition, but the amount of the composition perspray was adjusted to be 40 ml or 90 ml, the standard deviations ofiridium compositions in the catalyst layer were significantly increasedin comparison to those of Examples 1 and 2.

This is a result of the fact that, with respect to Examples 1 and 2according to the present invention, uniform catalyst layers can beformed at a faster rate by coating the compositions for forming acatalyst layer through electrostatic spray deposition and significantlymore uniform catalyst layers can be formed by coating the compositionsfor forming a catalyst layer through electrostatic spray deposition, butby allowing each composition to be coated in a predetermined amount perspray.

Experimental Example 2

A voltage measurement test was performed for each anode in chlor-alkalielectrolysis using a half cell to comparatively analyze performance ofeach anode prepared in the examples and comparative examples. In thiscase, samples having a size of 2 cm in length and 2 cm in width (P1) anda size of 1 cm in length and 1 cm in width (P2) were randomly sampledfrom two positions in each anode of the examples and comparativeexamples and respectively used as an anode of each half cell.

A 305 gpl (g/l) NaOH aqueous solution and 4.13 nM HCl were used as anelectrolyte, a platinum (Pt) wire was used as a counter electrode, andan SCE (Saturated Calomel electrode) was used as a reference electrode.The counter electrode, the reference electrode, and each anode were putin the electrolyte, a voltage of the anode was measured at a currentdensity of 4.4 kA/m² by constant current chronopotentiometry, and theresults thereof are presented in Table 2 and FIG. 1.

TABLE 2 Anode voltage (V vs. SCE), 4.4 kA/m² Category P1 P2 AverageExample 1 1.246 1.256 1.251 Example 2 1.257 1.253 1.255 Comparative1.245 1.312 1.278 Example 1 Comparative 1.247 1.286 1.267 Example 2Comparative 1.293 1.250 1.272 Example 3

As illustrated in Table 2 and FIG. 1, it was confirmed that averageovervoltages of the anodes of Examples 1 and 2 according to theembodiment of the present invention were reduced in comparison to thoseof Comparative Examples 1 to 3.

Also, when a voltage difference between P1 and P2 was examined,Comparative Examples 1 to 3 had large voltage differences, but, withrespect to Examples 1 and 2, the voltage differences were small anduniform.

From these results, with respect to the anodes of Examples 1 and 2according to the present invention, the active material can be uniformlydistributed in the catalyst layer, and thus, it can be confirmed thatthe overvoltage was reduced while exhibiting high efficiency.

Experimental Example 3

A degree of increase in electrolysis voltage of each anode prepared inthe examples and comparative examples was measured to comparativelyanalyze durability (lifetime).

In this case, samples having a size of 2 cm in length and 2 cm in width(P1) and a size of 1 cm in length and 1 cm in width (P2) were randomlysampled from two positions in each anode of the examples and comparativeexamples and respectively used as an anode for analyzing durability.

1 M Na₂SO₄ was used as an electrolyte and a Pt wire was used as acounter electrode to measure voltage rise time of the anode at a currentdensity of 40 kA/m², and the results thereof are presented in Table 3.

TABLE 3 Durability (hours) Category P1 (2 × 2) P2 (1 × 1) Example 1 2731 Example 2 24 27 Comparative 21 29 Example 1 Comparative 17 24 Example2 Comparative 18 26 Example 3

As illustrated in Table 3, it was confirmed that the anodes of Examples1 and 2 according to the embodiment of the present invention exhibiteduniform durability (lifetime), but the anodes of Comparative Examples 1to 3 had a large difference in durability depending on the sampledpositions.

From these results, with respect to the anodes of Examples 1 and 2according to the present invention, it was confirmed that the activematerial can be uniformly distributed in the catalyst layer, and thus,the lifetime can be improved.

1. An anode for electrolysis, the anode comprising: a metal base; and acatalyst layer comprising ruthenium oxide, iridium oxide, palladiumoxide, and titanium oxide on at least one surface of the metal base,wherein when the catalyst layer is equally divided into a plurality ofpixels, a uniform distribution of active material in the catalyst layeris achieved as indicated by a standard deviation of iridium compositionsof the plurality of divided pixels of 0.35 mol % or less.
 2. The anodefor electrolysis of claim 1, wherein the standard deviation of theiridium compositions is 0.2 mol % or less.
 3. The anode for electrolysisof claim 1, wherein the catalyst layer comprises 7.5 g or more ofruthenium metal component of the ruthenium oxide per unit area (m²) ofthe catalyst layer.
 4. The anode for electrolysis of claim 1, whereinthe catalyst layer comprises the ruthenium oxide, the iridium oxide, thetitanium oxide, and the palladium oxide in a molar ratio of from25:10:35:2 to 35:25:50:15 based on the metal components of the oxides.5. The anode for electrolysis of claim 1, wherein the catalyst layercomprises the palladium oxide in a molar ratio of 2 to 20 based on totalmoles of the ruthenium oxide, the iridium oxide, and the titanium oxide.6. The anode for electrolysis of claim 1, wherein the catalyst layerfurther comprises niobium oxide.
 7. An anode for electrolysis, the anodecomprising: a metal base; and a catalyst layer on at least one surfaceof the metal base, wherein: the catalyst layer comprises a platinumgroup oxide and titanium oxide, wherein the platinum group oxidecomprises ruthenium oxide, iridium oxide, and palladium oxide, a molarratio of the platinum group oxide to the titanium oxide is in a range of90:10 to 40:60, a molar ratio of the ruthenium oxide to the iridiumoxide is in a range of 90:10 to 50:50, a molar ratio of the palladiumoxide to the ruthenium oxide and the iridium oxide is in a range of 5:95to 40:60, when the catalyst layer is equally divided into a plurality ofpixels, a uniform distribution of active material in the catalyst layeris achieved as indicated by a standard deviation of iridium compositionsof the plurality of divided pixels of 0.35 mol % or less, and the anodewhen used for brine electrolysis has reduced overvoltage and generates 8g/l or more of hypochlorite.
 8. The anode for electrolysis of claim 1,wherein the metal base comprises titanium, tantalum, aluminum, hafnium,nickel, zirconium, molybdenum, tungsten, stainless steel, or an alloythereof.
 9. A method of preparing the anode for electrolysis of claim 1,the method comprising: coating a composition for forming a catalystlayer comprising a ruthenium oxide precursor, an iridium oxideprecursor, a palladium oxide precursor, and a titanium oxide precursoron at least one surface of a metal base, wherein the coating isperformed by electrostatic spray deposition in which an amount of thecomposition for forming a catalyst layer per spray and a spray rate areadjusted to be in ranges of 50 ml to 80 ml and 20 ml/min to 35 ml/min,respectively; drying the coating; and heat-treating the coating.
 10. Themethod of claim 9, wherein the preparation method further comprisesperforming a pretreatment of the metal base before coating with thecomposition for forming a catalyst layer, wherein the pretreatmentcomprises formation of irregularities on the surface of the metal baseby a chemical etching, blasting, or thermal spraying.
 11. The method ofclaim 9, wherein the composition for forming a catalyst layer isprepared by dissolving the ruthenium oxide precursor, the iridium oxideprecursor, the palladium oxide precursor, and the titanium oxideprecursor in an alcohol solution.
 12. The method of claim 9, wherein thecoating, drying, and heat-treating of the composition for forming acatalyst layer are sequentially repeated so that an amount of rutheniummetal component of the ruthenium oxide per unit area (m²) of the metalbase is 7.5 g or more.
 13. The method of claim 9, wherein thecomposition for forming a catalyst layer further comprises a niobiumoxide precursor.
 14. The anode for electrolysis of claim 7, wherein themetal base comprises titanium, tantalum, aluminum, hafnium, nickel,zirconium, molybdenum, tungsten, stainless steel, or an alloy thereof.